#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<math.h>
int main() {
	float L;
	int sum;
	int a;
	scanf("%f", &L);
	if (L <= 3)
	{
		sum = 10;
		a = sum;
		printf("%d", a);
	}
	else
	{
		sum = 10 + (L - 3) * 2;
		a = sum;
		printf("%d",a);
	}
	return 0;
}